The present invention relates generally to operations performed and equipment utilized in conjunction with a subterranean well and, in particular, to a safety valve with a built-in lockout feature.
Subsurface safety valves are well known in the oil and gas industry and act as a failsafe to prevent the uncontrolled release of reservoir fluids in the event of a worst-case scenario surface disaster. Typical subsurface safety valves are flapper-type valves which are opened and closed with the help of a flow tube moving telescopically within the production tubular. The flow tube is often controlled hydraulically from the surface and is forced into its open position using a piston and rod assembly that may be hydraulically charged via a control line linked directly to a hydraulic manifold or control panel at the well surface. When sufficient hydraulic pressure is conveyed to the subsurface safety valve via the control line, the piston and rod assembly forces the flow tube downward, which compresses a spring and simultaneously pushes the flapper downward to the open position. When the hydraulic pressure is removed from the control line, the spring pushes the flow tube back up, which allows the flapper to move into its closed position.
Some safety valves are arranged thousands of feet underground and are therefore required to traverse thousands of feet of borehole, including any turns and/or twists formed therein, before arriving at its proper destination. Consequently, during its descent downhole, the control line may undergo a substantial amount of vibration or otherwise sustain significant damage thereto. In extreme cases, the control line may be severed or one of the connection points for the control line may become inadvertently detached either at a surface well head or at the safety valve itself, thereby rendering the safety valve powerless. Moreover, during prolonged operation in downhole environments that exhibit extreme pressures and/or temperatures, the hydraulic actuating mechanisms used to move the flow tube may fail due to mechanical failures such as seal wear or the like. As a result, some safety valves prematurely fail, thereby leading end users to request the ability to lock the damaged safety valve in the open position.